An online automatic feedback system has been successfully installed and commissioned at the BL08U1A Soft X-ray Spectromicroscopy Beamline of Shanghai Synchrotron Radiation Facility, which can monitor the incident X-ray beam in real time by measuring the blade-edge signals of the exit slit and automatically adjust the elliptical cylindrical mirror parameters to achieve beam calibration and maintain the optimal X-ray flux of the sample. This work provides a comprehensive description of the hardware composition, system implementation, feedback logic, function and software design, system optimization and commission, as well as the online experimental results supported by the system. The experimental results demonstrated that the online automatic feedback system is capable of effectively maintaining the optimal X-ray beam flux for X-ray absorption spectroscopy experiments. Its success can provide valuable technique assistance for the design, construction and optimization of similar systems at various beamlines in synchrotron sources in the future.

The x-ray free-electron laser facilities are large-scale scientific experimental projects developed internationally in recent years, characterized by an ultrahigh repetition rate up to megahertz-level and ultrahigh brightness with a single-pulse flux of up to 1015 photons. Such high-performance facilities are equipped with optical transport systems exceeding one kilometer in length, where any adjustment deviation of optical components may lead to significant beam misalignment downstream. In order to protect downstream optical elements from damage caused by mis-steered high-repetition-rate photon pulses, two photon beam loss monitor systems are presented in this paper. By employing high-sensitivity detectors and ultrafast electronics, the system achieves comprehensive performance featuring rapid response, high stability, and strong protective capability. Experiment conducted at Shanghai Soft X-ray Free-Electron Laser Facility demonstrates that the system response time is faster than 1 μs, and it can accurately respond to single-pulse with power as low as 21 nJ. The development of this photon beam loss monitor system provides critical technical support and reliable safeguarding for the safe operation of free-electron laser facilities.